I thought of that, but that bike doesn't have that many miles on it, even taking the wear of the sand roads into consideration, and there's no visible signs of undue wear. Taking out a link only changes the total length of the chain, it doesn't change the length of the individual links nor their relationship to the chainring and gear.
One thing I have thought of that may be exacerbating the problem is my using cheap chains.
It's only happening on this one bike. I haven't run into this with the derailleur bikes. Although the road bike almost never gets ridden on sand, but the others do.